Manipulating Paths

Manipulating Paths

• Producing congruent paths and exporting to gpx
• Joining paths
• Reversing paths
• Backwards compatibility

Producing congruent paths and exporting to gpx

After paths have been corrected in GoogleEarth and saved, the original set of points has to be fitted to the new path. GEOrgET does this by recognising at least one unchanged point. Using these unchanged points as references, GEOrgET then interpolates the changed points. Removed points are treated as breaks; added or changed points are simply added at the end of the last known reference points at the regular time interval as determined by reading through the old points list until a break is reached. Points added to the beginning or end of a path are simply added at the standard time interval.

To synchronise the path list with the old points, navigate to the directory where the kml file resides and check its box. Then choose menu point 1. Produce congruent path and points (after moving, deleting or adding points). If it is necessary to change the time zone or starting time, these elements (Overwrite time zone and Overwrite date and time) should also be checked and the corresponding values selected.

GEOrgET produces a new file which bears the suffix "_00"; if suffixed files are present, then the program attempts to find the next higher number that is not present in the directory and names the file accordingly. In this way no file is overwritten.

Checking several files will process each of them sequentially.

Once congruent, files can also be exported to the gpx format for use in GPS devices. Check the box for Export to GPX.

Joining paths

Using a similar principle GEOrgET will take the paths from two files and combine them according to the data in the points list. If the two files are consecutive in time, then the time points will remain unchanged; however if the file was recorded later than a subsequent file, then the time data will be extrapolated as a series of points at the standard recording interval of the first file until a break is reached. Thus it really only makes sense to have the files in their correct temporal order, or to change the starting times so that they do form a continuous temporal order.

The name for the new file will not be derived from the parent files but has to be entered by the user.
Special features of the kml file, such as waypoints, rivers, lakes, shorelines, and their icons are checked for duplicates, and all uniquely present points are merged in the new file.

To be joined all files must be present in the same directory. By choosing more than one file, the Input files and Target file boxes under 2. Join paths become editable. Note that the order of files in the Input Files box is the order that they will be added to the first file in the list. Then choose point 2 and process.

Reversing paths

Finally, a path can be reversed, resulting in the reversal of all of its points. The time range remains unchanged, but the sequence of intervals will be reversed, i.e. if the second last interval was 30 s, and the last 20 s, then the first interval will be 20 s and the second 30 s. In this way, the temporal structure is preserved.

Checking more than one file results in each file being reversed. Reversed files are named with the suffix "_rv", and may overwrite existing files.

Choose 3. Reverse path from the menu.

Backwards compatibility

As long as a KML file contains a folder with a placemark in it, and that placemark contains the path, then the functions of making the path congruent, reversing it, and joining it are available. In this sense, GEOrgET is backwards compatible, i.e. it will take files that were generated by other means—even if the time data are not present—and still be able to work with them.